Filtration systems for treatment of polluted water include submerged aerated biological filters (SABF) which comprise a submerged bed of an inert particulate material on which micro-organisms which are responsible for treatment of contaminants within the water are attached. Waste water is passed through the fixed bed and the micro-organisms adsorb soluble or particulate pollution and subsequently aerobically degrade this material producing carbon dioxide, water, and additional cellular mass. Air is passed through the bed to provide oxygen to the micro-organisms.
Conventional particulate types for the bed include expanded clays and, in systems with floating media, polystyrene. Typically relatively coarse granular material, having an effective size of about 3 mm is used in systems having “deep beds”, typically beds having a depth greater than about 2.5 m. Waste water may flow either in a counter current to an air supply (down-flow) or co-current to an air supply (up-flow).
In addition to providing attachment sites for micro-organisms, the filter bed typically act as a mechanical filter, trapping suspended solids present in the waste water and trapping biomass debris. Over time, the filter bed becomes blocked or clogged by the growth of micro-organisms and suspended non-degradable solids, which cause a resistance to flow of water through the particulate material, resulting in an increase in hydraulic pressure required to drive the system. To remove excess cellular mass and solids captured within the filter bed, the bed is backwashed by introducing water to flush the solids from the beds The rate at which solids build up and pressure drop across the filter occurs determines the frequency with which the system requires to be backwashed, and backwash frequency is an important parameter in determining the overall efficiency of a filtration system.
Any discussion of documents, publications, acts, devices, substances, articles, materials or the like which is included in the present specification has been done so for the sole purpose so as to provide a contextual basis for the present invention. Any such discussions are not to be understood as admission of subject matter which forms the prior art base portion, or any part of the common general knowledge of the relevant technical field in relation to the technical field of the present invention to which it extended at the priority date or dates of the present invention.